The Lock stone grants the holder the ability to perform the dance move "Lock". However, this stone's possession also grants the holder the ability to lock objects and people in time, freezing them forever.
Flash Beat never used this skill in any episode. However, Breakin briefly performs locking during his dance in the last episode, complete with the sounds of a door's lock and a clock chime.
A clock tower that was possessed by this stone began to perform leg-locks using the hands on the clock face. The clock also possessed the ability to fire lock-empowered laser beams, which can freeze whatever it hits in time.
Dance of Origin
"Locking" is a dance term referring to the act of freezing, or "locking" parts of your body in place. It is the origin of several known moves, such as the "pop n' lock" and "lockstep